Regenerative medicine has gotten a lot of attention as an innovative medical treatment, which enables basic remedy for damaged and/or defective cells, tissues, and organs. The regenerating tissue used for regenerative medicine, which is produced through the steps of collecting cells from the body of a patient or the other person; separating and purifying the collected cells in vitro, and growing and organizing the cells into tissue, is transplanted into the body of the patient. Tissue engineering, making advances yearly, has enabled the methods for forming one kind of cells into a sheet and for arranging several kinds of cells sterically to assemble an organ by artificial means to be developed.
To amplify therapeutic cells, in particular adherent cells in large quantities, an incubator large in area is useful. It is because adherent cells are amplified while expanding in the planar direction. On the other hand, it has a problem that as the area of an incubator becomes larger, its culture surface increasingly deforms; thereby, cells aggregate in a lower area, leading to deteriorated usage efficiency. As an effective technique for manipulating cells, electrophoresis has gotten attention. The systematic study and theoretical analysis of electrophoresis were set out by Pohl in 1970s (see Nonpatent Literature 1). Micro biological substances, such as bacteria and cells, have been already employed as a principal target to be manipulated since the initial study; accordingly, biotechnology is one of key applications of electrophoresis.
A dielectrophoretic force FDEP exerted on dielectric particles is given by the following equation 1 (see Nonpatent Literature 1). In the following paragraph, how to calculate is explained taking an example of dielectric particles being cells.[Mathematical formula 1]FDEP=2πα3∈0∈mRe[K]∇E2  (Formula 1)
Where a is the radius of a cell approximated to a spherical shape, ∈0: electric permittivity in vacuum, ∈m: specific electric permittivity in medium, E: electric field intensity, and ∇ is an operator representing a gradient. In this case, ∇E2, which is the gradient for the square of an electric field intensity (E2), indicates how degree E2 inclines at that point, namely, how suddenly the electric field spatially changes. K is called a Claudius-Mossotti number and is represented by an equation 2. Herein, assuming that ∈b* and ∈m* be complex dielectric constants for cells and a medium, respectively, and Re [K] be the real part of the Claudius-Mossotti number, Re [K]>0 represents positive electrophoresis and the cells migrate in the same direction as that of the electric field gradient, namely toward an electric field concentration part. Re [K]<0 represents negative electrophoresis and cells migrate in the direction apart from the electric field concentration part, namely toward a weak electric field part.
                    [                  Mathematical          ⁢                                          ⁢          formula          ⁢                                          ⁢          2                ]                                                            K        =                                            ɛ              b              *                        -                          ɛ              m              *                                                          ɛ              b              *                        +                          2              ⁢                                                          ⁢                              ɛ                m                *                                                                        (                  Formula          ⁢                                          ⁢          2                )            
Formula 3 generally represents complex dielectric constant ∈r*.
                    [                  Mathematical          ⁢                                          ⁢          formula          ⁢                                          ⁢          3                ]                                                                      ɛ          r          *                =                              ɛ            r                    -                      j            ⁢                          σ                              ω                ⁢                                                                  ⁢                                  ɛ                  0                                                                                        (                  Formula          ⁢                                          ⁢          3                )            
Where, ∈r is the specific electric permittivity for a cell or medium, σ is the electric conductivity of a cell or medium, and ω is the angular frequency of an applied electric field. As known from Formulae 1, 2, and 3, a dielectrophoretic force depends on the radius of a cell, the real part of a Claudius-Mossotti number, and an electric field intensity. Moreover, it is known that the real part of the Claudius-Mossotti number varies depending on the complex electric permittivity and electric field frequency of a cell and medium.
The DEPIM method, combining dielectrophoresis and impedance measurement, has been proposed as a method for measuring microbial counts using dielectrophoresis. The DEPIM method is characterized in that these parameters are appropriately selected and a positive dielectrophoretic force exerted on microorganisms is sufficiently increased to collect the microorganisms into an electrode gap, making electrical measurement to determine a microbial count in the sample solution (see Nonpatent Literature 2).
In addition, a culture device, which eliminates unnecessary cells from a cell suspension using negative dielectrophoresis to culture necessary cells at high concentrations, is disclosed (see Patent Literature 1 and Patent Literature 3).
Moreover, a method and apparatus, for collecting cells efficiently in a target area without losing the activity of functional cells using positive dielectrophoresis, is disclosed (see Patent Literature 2).